Valve operating mechanism for internal combustion engine

ABSTRACT

A valve operating mechanism for operating a plurality of valves of a particular cylinder of an internal combustion engine includes a camshaft rotatable in synchronism with rotation of the internal combustion engine and having at least one cam. At least one of a plurality of cam followers slidably engages the cam for selectively operating the valves according to a cam profile of the cam. The cam followers are selectively interconnected and disconnected to operate the valves in different speed ranges of the internal combustion engine, the speed ranges including a range in which all of the valves remain inoperative. The camshaft has one or two annular raised portions in addition to the cam, and the cam followers include one or two cam followers which slidably engage the raised portion or portions. The valves remain inoperative by the annular portion or portions and are operated in a high-speed range by the cam, or selectively in low- and high-speed ranges by low- and high-speed ranges.

BACKGROUND OF THE INVENTION

The present invention relates to a valve operating mechanism for aninternal combustion engine, including a camshaft rotatable insynchronism with the rotation of the internal combustion engine andhaving integral cams for operating a pair of intake or exhaust valves,and rocker arms or cam followers angularly movable supported on a rockershaft for opening and closing the intake or exhaust valves in reponse torotation of the cams.

Japanese Laid-Open Patent Publication No. 59(1984)-226216, for example,discloses a valve operating mechanism for use in an internal combustionengine having a plurality of intake or exhaust valves per enginecylinder. Some of the intake or exhaust valves remain closed when theengine operates at a low speed. If the intake or exhaust valves of aparticular engine cylinder of a multicylinder internal combustion enginecould be kept inoperative in order to cut off the operation of theparticular engine cylinder, fuel consumption would be reduced bystopping the operation of the intake or exhaust valves of the particularengine cylinder while the engine operates in a low-speed range. However,no satisfactory devices have been available in the part to achieve sucha task.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a valve operatingmechanism for an internal combustion engine, which is of a relativelysimple structure, for making the intake or exhaust valves of aparticular engine cylinder inoperative for better fuel economy.

According to the present invention, there is provided a valve operatingmechanism for operating a plurality of valves of a particular cylinderof an internal combustion engine, comprising a camshaft rotatable insynchronism with rotation of the internal combustion engine and havingat least one cam, a plurality of cam followers at least one of whichslidably engages the cam for selectively operating the valves accordingto a cam profile of the cam, and means for selectively interconnectingand disconnecting the cam followers to operate the valves in differentspeed ranges of the internal combustion engine, the speed rangesincluding a range in which all of the valves remain inoperative.

The camshaft has one or two annular raised portions in addition to thecam, and the cam followers include one or two cam followers whichslidably engage the raised portion or portions. The valves remaininoperative by the annular portion or portions and are operated in ahigh-speed range by the cam, or selectively in low- and high-speedranges by low- and high-speed cams.

The above and other objects, features and advantages of the presentinvention will become more apparent from the following description whentaken in conjunction with the accompanying drawings in which preferredembodiments of the present invention are shown by way of illustrativeexample.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional view of a valve operating mechanismaccording to an embodiment of the present invention, the view beingtaken along line I--I of FIG. 2;

FIG. 2 is a plan view of the valve operating mechanism shown in FIG. 1;

FIG. 3 is a cross-sectional view taken along line III--III of FIG. 1,showing first and second cam followers connected to each other;

FIG. 4 is a cross-sectional view similar to FIG. 3, showing the firstand second cam followers disconnected from each other;

FIG. 5 is a vertical cross-sectional view of a valve operating mechanismaccording to another embodiment of the present invention, the view beingtaken along line V--V of FIG. 6;

FIG. 6 is a plan view of the valve operating mechanism shown in FIG. 5;

FIG. 7 is a cross-sectional view taken along line VII--VII of FIG. 6;

FIG. 8 is a cross-sectional view taken along line VIII--VIII of FIG. 5,showing first through third cam followers disconnected from each other;

FIG. 9 is a cross-sectional view similar to FIG. 8, showing the firstthrough third cam followers interconnected;

FIG. 10 is a plan view of a valve operating mechanism according to stillanother embodiment of the present invention; and

FIG. 11 is a plan view of a valve operating mechanism according to astill further embodiment of the present invention;

FIG. 12 is a cross-sectional view taken along line XII--XII of FIG. 11;

FIG. 13 is a cross-sectional view taken along line XIII--XIII of FIG.12, showing a mechanism for actuating the valve operating mechanism ofFIG. 11;

FIG. 14 is a plan view of a valve operating mechanism according to a yetstill further embodiment of the present invention; and

FIG. 15 is a cross-sectional view similar to FIGS. 8, 9 and 13, showinga mechanism for actuating the valve operating mechanism of FIG. 14.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Like or corresponding parts are denoted by like or correspondingreference characters throughout several views.

FIGS. 1 and 2 show a valve operating mechanism according to anembodiment of the present invention. The valve operating mechanism isincorporated in an internal combustion engine for use with a particularengine cylinder having a pair of intake valves 1a, 1b for introducing anair-fuel mixture into a combustion chamber defined in an engine body.

The valve operating mechanism comprises a camshaft 2 rotatable insynchronism with rotation of the engine at a speed ratio of 1/2 withrespect to the speed of rotation of the engine. The camshaft 2 has anannular raised portion 3 and a cam 5 which are integrally disposed onthe circumference of the camshaft 2. The valve operating mechanism alsohas a rocker shaft 6 extending parallel to the camshaft 2, and first andsecond rocker arms or cam followers 7, 8 angularly movably supported onthe rocker shaft 6 and held against the cam 5 and the raised portion 3,respectively, on the camshaft 2. The intake valves 1a, 1b remain closedor inoperative by the raised portion 3 in a low-speed range of theengine.

The camshaft 2 is rotatably disposed above the engine body. The raisedportion 3 is disposed in a position corresponding to an intermediateposition between the intake valves 1a, 1b, as viewed in FIG. 2. The cam5 is positioned substantially in line with the intake valve 1b. Theraised portion 3 has a circumferential profile in the shape of a circlecorresponding to the base circle 5b of the cam 5. The cam 5 has a camlobe 5a projecting radially outwardly from the base circle 5b.

The rocker shaft 6 is fixed below the camshaft 2. The first cam follower7 pivotally supported on the rocker shaft 6 is aligned with the cam 5,and the second cam follower 8 pivotally supported on the rocker shaft 6is aligned with the raised portion 3. The cam followers 7, 8 have ontheir upper surfaces cam slippers 7a, 8a, respectively, held in slidingcontact with the cam 5 and the raised portion 3, respectively. Thesecond cam follower 8 includes a pair of arms 8b, 8c having distal endspositioned above the intake valves 1a, 1b, respectively. Tappet screws12, 13 are threaded through the distal ends of the arms 8b, 8c and havetips engageable respectively with the upper ends of the valve stems ofthe intake valves 1a, 1b.

Flanges 14, 15 are attached to the upper ends of the valve stems of theintake valves 1a, 1b. The intake valves 1a, 1b are normally urged toclose the intake ports by compression coil springs 16, 17 disposed undercompression around the valve stems between the flanges 14, 15 and theengine body.

A bottomed cylindrical lifter 19 is disposed in abutment against a lowersurface of the first cam follower 7. The lifter 19 is normally urgedupwardly by a compression spring 20 of relatively weak resiliencyinterposed between the lifter 19 and the engine body for resilientlybiasing the cam slipper 7a of the first cam follower 7 slidably againstthe cam 5.

As illustrated in FIG. 3, the first and second cam followers 7, 8 haveconfronting side walls held in sliding contact with each other. Aselective coupling 21 is operatively disposed in and between the firstand second cam followers 7, 8 for selectively disconnecting the camfollowers 7, 8 from each other for relative displacement and also forinterconnecting the cam followers 7, 8 for their movement in unison.

The selective coupling 21 comprises a piston 23 movable between aposition in which it interconnects the first and second cam followers 7,8 and a position in which it disconnects the first and second camfollowers 7, 8 from each other, a circular stopper 24 for limiting themovement of the piston 23, and a coil spring 25 for urging the stopper24 to move the piston 23 toward the position to disconnect the first andsecond cam followers 7, 8 from each other.

The second cam follower 8 has a first guide hole 26 opening toward thefirst cam follower 7 and extending parallel to the rocker shaft 6. Thesecond cam follower 8 also has a smaller-diameter hole 28 near theclosed end of the first guide hole 26, with a step or shoulder 27 beingdefined between the smaller-diameter hole 28 and the first guide hole26. The piston 23 is slidably fitted in the first guide hole 26. Thepiston 23 and the closed end of the smaller-diameter hole 28 definetherebetween a hydraulic pressure chamber 29.

The second cam follower 8 has a hydraulic passage 30 defined therein incommunication with the hydraulic pressure chamber 29. The rocker shaft 6has a hydraulic passage 31 defined axially therein and coupled to asource (not shown) of hydraulic pressure through a suitable hydraulicpressure control mechanism. The hydraulic passages 30, 31 are held incommunication with each other through a hole 32 defined in a side wallof the rocker shaft 6, irrespective of how the second cam follower 8 isangularly moved about the rocker shaft 6.

The first cam follower 7 has a second guide hole 35 opening toward thesecond cam follower 8 in registration with the first guide hole 26 inthe second cam follower 8. The circular stopper 24 is slidably fitted inthe second guide hole 35. The first cam follower 7 also has asmaller-diameter hole 37 near the closed end of the second guide hole35, with a step or shoulder 36 defined between the second guide hole 35and the smaller-diameter hole 37 for limiting movement of the circularstopper 24. The first cam follower 7 also has a through hole 38 definedcoaxially with the smaller-diameter hole 37. A guide rod 39 joinedintegrally and coaxially to the circular stopper 24 extends through thehole 38. The coil spring 25 is disposed around the guide rod 39 betweenthe stopper 24 and the closed end of the smaller-diameter hole 37.

The piston 23 has an axial length selected such that when one end of thepiston 23 abuts against the step 27, the other end thereof is positionedjust between and hence lies flush with the sliding side walls of thefirst and second cam followers 7, 8, and when the piston 23 is movedinto the second guide hole 35 until it displaces the stopper 24 intoabutment against the step 36, said one end of the piston 23 remains inthe first guide hole 26 and hence the piston 23 extends between thefirst and second cam followers 7, 8. The piston 23 is normally urgedtoward the first cam follower 7 under the resiliency of a coil spring 33disposed in the hydraulic pressure chamber 29 and acting between thepiston 23 and the closed bottom of the smaller-diameter hole 28. Theresilient force of the spring 33 set under compression in the hydraulicpressure chamber 29 is selected to be smaller than that of the spring 25set in place under compression.

Operation of the valve operating mechanism will be described withreference to FIGS. 3 and 4. When the engine is to operate in a low-speedrange, the selective coupling 21 is actuated to disconnect the first andsecond cam followers 7, 8 from each other as illustrated in FIG. 4. Morespecifically, the hydraulic pressure is released by the hydraulicpressure control mechanism from the hydraulic pressure chamber 29, thusallowing the stopper 24 to move toward the second cam follower 8 underthe resiliency of the spring 25 until the piston 23 abuts against thestep 27. When the piston 23 engages the step 27, the mutually contactingends of the piston 23 and the stopper 24 lie flush with the sliding sidewalls of the first and second cam followers 7, 8. Therefore, the firstand second cam followers 7, 8 are held in mutually sliding contact forrelative angular movement.

With the first and second cam followers 7, 8 being thus disconnected,the first cam follower 7 is angularly moved in sliding contact with thecam 5, whereas the second cam follower 8 is held in sliding contact withthe raised portion 3. Since the raised portion 3 does not impose anycamming action on the second cam follower 8, the intake valves 1a, 1bremain closed. The swinging movement of the first cam follower 7 whichis caused by the cam 5 does not affect the intake valves 1a, 1b as thefirst cam follower 7 is disconnected from the second cam follower 8 atthis time. Any frictional loss of the valve operating mechanism isrelatively low because the first cam follower 7 is held in slidingcontact with the cam 5 under the relatively small resilient force of thespring 20.

During low-speed operation of the engine, therefore, the intake valves1a, 1b remain closed or inoperative for reducing fuel consumption.

For high-speed operation of the engine, the first and second camfollowers 7, 8 are interconnected by the selective coupling 21, as shownin FIG. 3. More specifically, the hydraulic pressure chamber 29 of theselective coupling 21 is supplied with hydraulic pressure to cause thepiston 23 to push the support 24 into the second guide hole 35 againstthe resiliency of the spring 25 until the stopper 24 engages the step36. The first and second cam followers 7, 8 are not connected to eachother for angular movement in unison.

At this time, the second cam follower 8 is caused to swing the first camfollower 7. Therefore, the intake valves 1a, 1b alternately open andclose the respective intake ports at the valve timing and valve liftaccording to the profile of the cam 5.

FIGS. 5 through 9 show a valve operating mechanism according to anotherembodiment of the present invention.

The valve operating mechanism comprises a camshaft 2 rotatable insynchronism with rotation of the engine at a speed ratio of 1/2 withrespect to the speed of rotation of the engine. The camshaft 2 has apair of annular raised portions 3 and a cam 5 which are integrallydisposed on the circumference of the camshaft 2, the cam 5 beingdisposed between the raised portions 3. The valve operating mechanismalso has a rocker shaft 6 extending parallel to the camshaft 2, andfirst through third cam followers 7, 8, 9 angularly movably supported onthe rocker shaft 6 and held against the cam 5 and the raised portions 3,respectively, on the camshaft 2. A pair of intake valves 1a, 1b remainsinoperative by the raised portions 3 in a low-speed range of the engine.

The camshaft 2 is rotatably disposed above the engine body. The cam 5 isdisposed in a position corresponding to an intermediate position betweenthe intake valves 1a, 1b, as viewed in FIG. 6. The raised portions 3 arepositioned substantially in line with the intake valves 1a, 1b,respectively. The raised portions 3 have a circumferential profile inthe shape of a circle corresponding to the base circle 5b of the cam 5.The cam 5 has a cam lobe 5a projecting radially outwardly from the basecircle 5b.

The rocker shaft 6 is fixed below the camshaft 2. The first cam follower7 pivotally supported on the rocker shaft 6 is aligned with the cam 5,and the second and third cam followers 8, 9 pivotally supported on therocker shaft 6 are aligned respectively with the raised portions 3. Thecam followers 7, 8, 9 have on their upper surfaces cam slippers 7a, 8a,9a, respectively, held in sliding contact with the cam 5 and the raisedportions 3, respectively. The second and third cam followers 8, 9 havedistal ends positioned above the intake valves 1a, 1b, respectively.Tappet screws 12, 13 are threaded through the distal ends of the camfollowers 8, 9 and have tips engagable respectively with the upper endsof the valve stems of the intake valves 1a, 1b.

Flanges 14, 15 are attached to the upper ends of the valve stems of theintake valves 1a, 1b. The intake valves 1a, 1b are normally urged toclose the intake ports by compression coil springs 16, 17 disposed undercompression around the valve stems between the flanges 14, 15 and theengine body.

A bottomed cylindrical lifter 19 is disposed in abutment against a lowersurface of the first cam follower 7. The lifter 19 is normally urgedupwardly by a compression spring 20 of relatively weak resiliencyinterposed between the lifter 19 and the engine body for resilientlybiasing the cam slipper 7a of the first cam follower 7 slidably againstthe cam 5.

As illustrated in FIG. 8, the first and second cam followers 7, 8 haveconfronting side walls held in sliding contact with each other. A firstselective coupling 21 is operatively disposed in and between the firstand second cam followers 7, 8 for selectively disconnecting the camfollowers 7, 8 from each other for relative displacement and also forinterconnecting the cam followers 7, 8 for their movement in unison.Likewise, the first and third cam followers 7, 9 have confronting sidewalls held in sliding contact with each other. A second selectivecoupling 22 is operatively disposed in and between the first and thirdcam followers 7, 9 for selectively disconnecting the cam followers 7, 9from each other for relative displacement and also for interconnectingthe cam followers 7, 9 for their movement in unison.

The first and second selective couplings 21, 22 are of an identicalconstruction, and hence only the first selective coupling 21 willhereinafter be described in detail.

The first selective coupling 21 comprises a piston 23 movable between aposition in which it interconnects the first and second cam followers 7,8 and a position in which it disconnects the first and second camfollowers 7, 8 from each other, a circular stopper 24 for limiting themovement of the piston 23, and a coil spring 25 for urging the stopper24 to move the piston 23 toward the position to disconnect the first andsecond cam followers 7, 8 from each other.

The first cam follower 7 has a first guide hole 26 opening toward thesecond cam follower 8 and extending parallel to the rocker shaft 6. Thefirst cam follower 7 also has a smaller-diameter hole 28 near the closedend of the first guide hole 26, with a step or shoulder 27 being definedbetween the smaller-diameter hole 28 and the first guide hole 26. Thepiston 23 is slidably fitted in the first guide hole 26. The piston 23and the closed end of the smaller-diameter hole 28 define therebetween ahydraulic pressure chamber 29.

The first cam follower 7 has a hydraulic passage 30 defined therein incommunication with the hydraulic pressure chamber 29. The rocker shaft 6has a hydraulic passage 31 defined axially therein and coupled to asoruce (not shown) of hydraulic pressure through a suitable hydraulicpressure control mechanism. The hydraulic passages 30, 31 are held incommunication with each other through a hole 32 defined in a side wallof the rocker shaft 6, irrespective of how the first cam follower 7 isangularly moved about the rocker shaft 6.

The second cam follower 8 has a second guide hole 35 opening toward thefirst cam follower 7 in registration with the first guide hole 26 in thefirst cam follower 7. The circular stopper 24 is slidably fitted in thesecond guide hole 35. The second cam follower 8 also has asmaller-diameter hole 37 near the closed end of the second guide hole35, with a step or shoulder 36 defined between the second guide hole 35and the smaller-diameter hole 37 for limiting movement of the circularstopper 24. The second cam follower 8 also has a through hole 38 definedcoaxially with the smaller-diameter hole 37. A guide rod 39 joinedintegrally and coaxially to the circular stopper 24 extends through thehole 38. The coil spring 25 is disposed around the guide rod 39 betweenthe stopper 24 and the closed end of the smaller-diameter hole 37.

The piston 23 has an axial length selected such that when one end of thepiston 23 abuts against the step 27, the other end thereof is positionedjust between and hence lies flush with the sliding side walls of thefirst and second cam followers 7, 8, and when the piston 23 is movedinto the second guide hole 35 until it displaces the stopper 24 intoabutment against the step 36, said one end of the piston 23 remains inthe first guide hole 26 and hence the piston 23 extends between thefirst and second cam followers 7, 8. The hydraulic passage 31 is sharedby the first and second selective couplings 21, 22, which are thereforeactuated simultaneously under fluid pressure supplied via the hydraulicpassage 31.

Operation of the valve operating mechanism will be described withreference to FIGS. 8 and 9. When the engine is to operate in a low-speedrange, the first and second selective couplings 21, 22 are actuated todisconnect the first through third cam followers 7, 8, 9 from each otheras illustrated in FIG. 8. More specifically, the hydraulic pressure isreleased by the hydraulic pressure control mechanism from the hydraulicpressure chamber 29, thus allowing the stopper 24 to move toward thefirst cam follower 7 under the resiliency of the spring 25 until thepiston 23 abuts against the step 27. When the piston 23 engages the step27, the mutually contacting ends of the piston 23 and the stopper 24 ofthe first selective coupling 21 lie flush with the sliding walls of thefirst and second cam followers 7, 9. Likewise, the mutually contactingends of the piston 23 and the stopper 24 of the second selectivecoupling 22 lie flush with the sliding side walls of the first and thirdcam followers 7, 9. Thus, the first, second, and third cam followers 7,8, 9 are held in mutually sliding contact for relative angular movement.

With the first through third cam followers 7, 8, 9 being thusdisconnected, the second and third cam followers 8, 9, which slidinglycontact the raised portions 3, are not angularly moved, keeping theintake valves 1a, 1b closed. The second and third cam followers 8, 9 arenot affected by the angular movement of the first cam follower 7 insliding contact with the cam 5. Any frictional loss of the valveoperating mechanism is relatively low because the first cam follower 7is held in sliding contact with the cam 5 under the relatively smallresilient force of the spring 20.

During low-speed operation of the engine, therefore, fuel consumption isreduced inasmuch as the intake valves 1a, 1b remain closed orinoperative.

When the engine is to operate at a high speed, the first through thirdcam followers 7, 8, 9 are interconnected by the first and secondselective couplings 21, 22, as shown in FIG. 9, by supplying hydraulicpressure into the hydraulic-pressure chambers 29 of the first and secondselective couplings 21, 22. More specifically, the pistons 23 are forcedby the supplied hydraulic pressure into the second guide holes 35 whilepressing the stoppers 24 against the resilient forces of the springs 25until the stoppers 24 are pressed against the steps 36. The firstthrough third cam followers 7, 8, 9 are interconnected by the first andsecond selective couplings 21, 22 so that they are caused to swing inunison by the cam 5. As a consequence, the intake valves 1a, 1balternately open and close the respective intake ports at the valvetiming and valve lift according to the profile of the cam 5.

FIG. 10 shows a valve operating mechanism according to still anotherembodiment of the present invention. The camshaft 2 has a cam 5 and apair of adjacent annular raised portions 3 disposed on one side of thecam 5. The first and third cam followers 7, 9 are held in slidingcontact with the raised portions 3, respectively, and engage the intakevalves 1a, 1b, respectively. The second cam follower 8 is held insliding contact with the cam 5. The intake valves 1a, 1b are controlledin different speed ranges by the mechanism shown in FIGS. 8 and 9. Inthe low-speed range, the intake valves 1a, 1b remain closed orinoperative since the first and third cam followers 7, 9 are notangularly moved. In the high-speed range, the intake valves 1a, 1b arecaused to alternately open and close their intake ports according to thecam profile of the cam 5.

According to a still further embodiment shown in FIGS. 11 and 12, thecamshaft 2 has an annular raised portion 3, a low-speed cam 4, and ahigh-speed cam 5 which are integrally disposed on the camshaft 2, theannular raised portion 3 being positioned between the low- andhigh-speed cams 4, 5. The raised portion 3 has a circumferential profilein the shape of a circle corresponding to the base circles 4b, 5b of thelow- and high-speed cams 4, 5. The low-speed cam 4 has a cam lobe 4aprojecting radially outwardly from the base circle 4b, and thehigh-speed cam 5 has a cam lobe 5a projecting radially outwardly fromthe base circle 5b to a greater extent than the cam lobe 4a, the camlobe 5a also having a larger angular extent than the cam lobe 4a.

The first cam follower 7 is held in sliding contact with the raisedportion 3, whereas the second and third cam followers 8, 9 are held insliding contact with the low- and high-speed cams 4, 5, respectively.The first cam follower 7 has a pair of arm ends engageable with theupper ends of the valve stems of a pair of intake valves 1a, 1b.

The first through third cam followers 7, 8, 9 shown in FIG. 11 areoperated by a mechanism as shown in FIG. 13. the structure of FIG. 13 issubstantially similar to that of FIGS. 8 and 9, except that a steel ball33 is forcibly fitted in the hydrualic passage 31 to divide it into twoindependent passages for separately operating the first and secondselective couplings 21, 22. In the low-speed range, the first throughsecond cam followers 7, 8, 9 are disconnected from each other as shownin FIG. 8, and hence the intake valves 1a, 1b remain closed as the firstcam follower 7 is not caused to swing. In the medium-speed range, thefirst and second cam followers 7, 8 are interconnected, while the firstand third cam followers 7, 9 are disconnected from each other, as shownin FIG. 13. Thus, the intake valves 1a, 1b are operated by the low-speedcam 4. In the high-speed range, the first through third cam followers 7,8, 9 are interconnected as shown in FIG. 9 to enable the intake valves1a, 1b to be operated by the high-speed cam 5.

FIG. 14 shows a valve operating mechanism according to a yet stillfurther embodiment of the present invention. In FIG. 14, the low-speedcam 4 is positioned between the high-speed cam 5 and the annular raisedportion 3. The first and second cam followers 7, 8 are held in slidingcontact with the low- and high-speed cams 4, 5, and the third camfollower 9 engaging the intake valves 1a, 1b is held in sliding contactwith the raised portion 3. The mechanism shown in FIG. 15, which issimilar to FIGS. 8 and 9 and identical to that of FIG. 13, is employedto control the intake valves 1a, 1b. In the low-speed range, the firstthrough second cam followers 7, 8, 9 are disconnected from each other asshown in FIG. 8, and hence the intake valves 1a, 1b remain closed. Inthe medium-speed range, the first and third cam followers 7, 9 areinterconnected, while the first and second cam followers 7, 8 aredisconnected from each other, as shown in FIG. 15. Thus, the intakevalves 1a, 1b are operated by the low-speed cam 4. In the high-speedrange, the first through third cam followers 7, 8, 9 are interconnectedas shown in FIG. 9 to operate the intake valves 1a, 1b according to thecam profile of the high-speed cam 5.

While the intake valves 1a, 1b are shown as being operated by each ofthe valve operating mechanisms, exhaust valves may also be operated bythe valve operating mechanisms according to the present invention. Insuch a case, unburned components due to exhaust gas turbulence can bereduced in low-speed operation of the engine, whereas high engine outputpower and torque can be generated by reducing resistance to the flow ofan exhaust gas from thee combustion chamber in high-speed operation ofthe engine.

Although certain preferred embodiments have been shown and described, itshould be understood that many changes and modifications may be madetherein without departing from the scope of the appended claims.

We claim:
 1. A valve operating mechanism for operating a plurality ofvalves of a particular cylinder of an internal combustion engine,comprising:a camshaft rotatable in synchronism with rotation of theinternal combustion engine and having at least one cam; a plurality ofcam followers, one of which slidably engages with said cam forselectively operating the valves according to a cam profile of said cam;and means for selectively interconnecting and disconnecting said camfollowers to operate the valves differently in different speed ranges ofthe internal combustion engine, said speed ranges including a range inwhich all of the valves remain inoperative.
 2. A valve operatingmechanism according to claim 1, wherein said camshaft has two annularraised portions with one positioned on each said of said cam, said camfollowers including cam followers which slidably engage said raisedportions, respectively, for controlling said valves, said meansincluding means for selectively keeping said valves inoperative in saidrange with said raised portions and operating said valves in ahigh-speed range with said cam.
 3. A valve operating mechanism accordingto claim 1, wherein said camshaft has an annular raised portionpositioned adjacent to said cam, said cam followers including a camfollower which slidably engages said raised portion for controlling saidvalves, said means including means for selectively keeping said valvesinoperative in said range with said raised portion and operating saidvalves in a high-speed range with said cam.
 4. A valve operatingmechanism according to claim 1, wherein said camshaft has two adjacentannular raised portions positioned on one side of said cam, said camfollowers including cam followers which slidably engage said raisedportions, respectively, for controlling said valves, said meansincluding means for selectively keeping said valves inoperative in saidrange with said raised portions and operating said valves in ahigh-speed range with said cam.
 5. A valve operating mechanism accordingto claim 1, wherein said camshaft has an annular raised portion, alow-speed cam, and a high-speed cam, said raised portion beingpositioned between said low- and high-speed cams, said cam followersincluding cam followers which slidably engage said low- and high-speedcams, respectively, and a cam follower which slidably engages saidraised portion for controlling said valves, said means including meansfor selectively keeping said valve inoperative in said range with saidraised portion and operating said valves in a low-speed range with saidlow-speed cam and in a high-speed range with said high speed cam.
 6. Avalve operating mechanism according to claim 1, wherein said camshafthas an annular raised portion, a low-speed cam, and a high-speed cam,said low-speed cam being positioned between said raised portion and saidhigh-speed cams, said cam followers including cam followers whichslidably engage said low- and high-speed cams, respectively, and a camfollower which slidably engages said raised portion for controlling saidvalves, said means including means for selectively keeping said valvesinoperative in said range with said raised portion and operating saidvalves in a low-speed range with said low-speed cam and in a high-speedrange with said cam.
 7. A valve operating mechanism for operating aplurality of valves of a particular cylinder of an internal combustionengine, comprising:a camshaft carrying an annular raised portion formaintaining said valves in a closed condition and cam means having a camprofile for sequentially opening and closing said valves, first camfollower means slidably engaging said raised portion and operativelyconnecting said valves thereto, second cam follower means slidablyengaging said cam means, and means for selectively interconnecting anddisconnecting said first and second cam followers at a predeterminedcondition of engine operation whereby said raised portion is effectiveto operate said valves during one range of engine operation and said cammeans is effective to operate said valves during another range of engineoperation.
 8. A valve operating mechanism as recited in claim 7 in whichsaid cam means includes a cam profile comprising a base circle and a camlobe extending radially therefrom and said annular raised portion has adiameter corresponding substantially to that of said base circle.
 9. Avalve operating mechanism as recited in claim 8 in which said first camfollower means is a bifurcate member effective to operatively connectsaid valves to said raised portion.
 10. A valve operating mechanism asrecited in claim 9 in which said cam means includes a low-speed and ahigh-speed cam and said interconnecting and disconnecting meansincluding means for connecting and disconnecting said second camfollower means to said first cam followers means for operation of saidfirst cam follower means in response to either said raised portion, saidlow-speed cam or said high-speed cam.
 11. A valve operating mechanism asrecited in claim 10 in which said interconnecting and disconnectingmeans are effective to selectively connect said first cam follower meanswith the adjacent second cam follower means.
 12. A valve operatingmechanism as recited in claim 11 in which said first cam follower meansis positioned intermediate the respective of said second cam followermeans and said interconnecting and disconnecting means are effective toselectively connect said first cam follower means with either or both ofsaid respective second cam follower means.